1. Field of the Invention
This invention relates to refrigeration apparatus and in particular to means for sensing the temperature within a refrigerated space for the purpose of controlling the refrigeration apparatus or for controlling an over-temperature indicator.
2. Description of the Background Art
In a conventional refrigeration apparatus having a compartment refrigerated by suitable refrigerating means, operation of the refrigerating means is typically controlled by a sensor which senses the temperature of the compartment, to cause refrigeration thereof when the temperature rises to a preselected temperature. In one form of such apparatus, the temperature sensor is carried by the door of the refrigeration apparatus.
A problem arises when using a door-mounted temperature sensor in that the temperature to which the sensor is exposed and the temperature of the refrigerated compartment may increase rapidly toward the ambient temperature when the door is opened for a period of time, even though the objects being refrigerated within the compartment do not rise in temperature as rapidly as the air temperature therein. As a result of the temperature sensor in the door being exposed to the relatively higher temperature ambient air and compartment air, the sensor output may not be reliable for purposes of operating an over-temperature alarm or controlling the refrigeration apparatus.
This condition is aggravated when the refrigeration apparatus is being operated in a relatively high ambient temperature. For example, in a conventional refrigeration apparatus having an over-temperature alarm and a sensor operating at a fixed trip point, it is desirable to set the alarm to operate at a sensed temperature of approximately 60.degree. F. The 60.degree. F. trip point is necessary even though the compartment is normally maintained at 34.degree. F.-38.degree. F., in order to prevent unnecessary alarm indications from being given as a result of the high ambient temperature. Where the refrigeration apparatus is provided in an environment of relatively low ambient temperature, the relatively high temperature trip point is undesirable. Under such lower ambient temperature conditions, it would be desirable to lower the trip point to provide a more sensitive operation of the over-temperature indicator.
A number of refrigeration apparatus controls have been developed over the years which are concerned with the problem of controlling the operation of the refrigeration apparatus as a function of sensed temperature. Illustratively, Raymond J. Ridge, in U.S. Pat. No. 2,148,643, shows a refrigerator control having a sensing bulb for sensing the temperature of the evaporator and a bimetallic sensing device within a control mechanism remote from the sensing bulb and subject to air delivered from the rear of the refrigeration apparatus. The control is arranged so that a snap-acting mechanism is caused to have its action varied with changes in ambient temperature so as to vary the temperature at which the evaporator sensing element is effective in controlling the operation of the refrigeration apparatus. The apparatus is provided with an access door remotely spaced from the sensing elements and switch.
In U.S. Pat. No. 3,707,851, Robert B. McAshan, Jr. shows a refrigeration system having first and second sensing means, such as thermistors. One of the thermistors senses the ambient temperature conditions and the other of the thermistors senses the temperature of the refrigerant in the refrigeration system.
Ko Toya, in U.S. Pat. No. 3,977,851, shows an automatic electronic ice-making control system also utilizing a thermistor as a sensing element for terminating an ice-making cycle. A second variable resistance element compensates the characteristics of the thermistor in accordance with ambient temperature conditions to provide an output signal so as to terminate ice-making operation upon production of substantially the same quantity of ice independent of the season of the year during which the ice-making machine is operative.